This invention relates to an automatic photoflash device and more particularly to an automatic photoflash device informing the operator of an insufficient exposure.
In an automatic photoflash device, a flash tube is triggered in response to a synchronizing signal to radiate a light flash by the discharge of a main capacitor. When a proper exposure is obtained, the electrical energy charged in a quenching capacitor backward biases the main thyristor connected in series with the main capacitor, rendering the main thyristor nonconducting and interrupting the flash radiation of the flash tube. Where, however, an insufficient charge of the main capacitor causes the flash tube to fall to emit a light flash or emit an insufficient light flash, then proper exposure can not be effected. Further where the quenching capacitor is incompletely charged, then the photoflash device cannot interrupt a light fash, probably resulting in an overexposure. The failure to interrupt a light flash takes place particularly where an object is photographed by a photoflash device at a short distance. In the case of photographing at a short distance, the quenching capacitor is discharged, but the main capacitor is little discharged. Where, therefore, the flash tube is flashed frequently at a short interval, then it becomes impossible to interrupt a light flash.
It is accordingly the object of this invention to provide an automatic photoflash device which definitely indicates complete readiness for the normal radiation of a light flash and the termination of the light flash.